Secondary battery, battery pack, electronic apparatus, electric tool, electric vehicle, and power storage system

ABSTRACT

A secondary battery including: spirally wound electrode body in which positive electrode and negative electrode are laminated via separator and spirally wound, wherein the positive electrode includes an inner circumference side positive electrode active material layer and an outer circumference side positive electrode active material layer while including a single side active material layer formation region, the ratio A/(A+B) of an area density A (mg/cm 2 ) of the inner circumference side positive electrode active material layer and an area density B (mg/cm 2 ) of the outer circumference side positive electrode active material layer, an inner diameter C (mm) of the coil opening portion, and the ratio D/E of a thickness D (μm) of the positive electrode and a thickness E (μm) of the positive electrode collector satisfy the relationship expressed in Formula 1, and a length F (mm) of the single side active material layer formation region satisfies the relationship expressed in Formula 2.

CROSS REFERENCES TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 13/312,521, filed on Dec. 6, 2011, which claims priority toJapanese Priority Patent Application JP 2010-276716 filed in the JapanPatent Office on Dec. 13, 2010, the entire content of which is herebyincorporated by reference.

BACKGROUND

The present application relates to a secondary battery that includes aspirally wound electrode body in which a positive electrode and anegative electrode are laminated and spirally wound via a separator, anda battery pack, an electronic apparatus, an electric tool, an electricvehicle, and a power storage system that use such a secondary battery.

In recent years, electronic apparatuses typified by mobile terminalapparatuses and the like have been popularized, and there is demand forsuch apparatuses to be further miniaturized, lightened, and to have alonger service life. Accordingly, the development of a battery,particularly a secondary battery that is small, light, and able toobtain a high energy density as a power source has been pursued.Further, with secondary batteries, application for uses in large sizessuch as for automobiles is also being considered, and wide applicationsfor other uses is also being considered.

As a secondary battery, the use of a variety of elements as the carrier(material that reciprocates between the positive electrode and thenegative electrode during charging and recharging) is being researched.Among such secondary batteries, there are great expectations on asecondary battery that uses lithium as the carrier, specifically, alithium ion secondary battery that uses the absorption and the dischargeof the lithium as a charging and discharging reaction. The reason isthat it is possible to obtain a higher energy density than a leadbattery or a nickel cadmium battery.

A secondary battery includes a spirally wound electrode body that is theso-called cell element, and the spirally wound electrode body iscomposed by a positive electrode and a negative electrode that arelaminated via a separator and spirally wound. The positive electrodeincludes a positive electrode active material layer that is formed on apositive electrode collector, and the negative electrode includes anegative electrode active material layer that is formed on a negativeelectrode collector.

Incidentally, recently, accompanying the rapid increase in performanceand functionality of electronic apparatuses and the like, there is astrong demand to further improve the performance of secondary batteries,particularly to increase capacity. Accompanying such a demand, in orderto increase the charging and discharging capacity of a positiveelectrode and a negative electrode, if a high capacity material is usedas the negative electrode active material that is included in thenegative electrode active material layer, there is accordingly cause toincrease the thickness of the positive electrode active material layer.Further, in order to increase the volume occupied by the positiveelectrode and the negative electrode in the secondary battery, if thethickness of the positive electrode collector and the separator arereduced, the thicknesses of the positive electrode active material layerand the negative electrode active material layer are accordinglyincreased.

However, if the thickness of the positive electrode active materiallayer is increased, the flexibility of the positive electrode activematerial layer thereof decreases. Therefore, if the positive electrodeis spirally wound around a coil core rod along with the negativeelectrode and the like when creating the spirally wound electrode body,the positive electrode in the vicinity of the center where the radius ofcurvature is small becomes prone to fracturing. Such a tendency becomesparticularly striking the smaller the outer diameter of the coil corerod is made in order to increase the volume occupied by the positiveelectrode and the negative electrode within the secondary battery.

Therefore, in order to suppress fracturing of the positive electrodewhen coiling, a variety of countermeasures and related techniques havebeen proposed. Specifically, when creating a flat coil group composed ofsubstantially straight portions and curved portions by coiling apositive electrode plate or the like, causing a solvent to contactportions that correspond to the curved portions of the positiveelectrode plate and lowering the positive electrode plate density of thecurved portions to be lower than the positive electrode plate density ofthe substantially straight portions has been proposed (for example,refer to Japanese Unexamined Patent Application Publication No.2005-310617). Causing the application thickness of an electrode compoundthat is applied to the inside to be thinner than the applicationthickness of the electrode compound that is applied to the outside whencoiling a sheet-shaped electrode is proposed (for example, refer toJapanese Unexamined Patent Application Publication No. 08-130035).Including a predetermined amount of a copolymer of vinylidene fluoride,tetrafluoroethylene, and hexafluoropropylene as a binder on the positiveelectrode active material layer has been proposed (for example, refer toJapanese Unexamined Patent Application Publication No. 2006-059771). Outof the binder layers (inner circumference layer and outer circumferencelayer) that are provided on both sides of the collector, causing thethickness of the outer circumference layer to be greater than thethickness of the inner circumference layer and causing the activematerial amount of the outer circumference side to be greater than theactive material amount of the inner circumference layer has beenproposed (for example, refer to Japanese Patent No. 3131976). In apositive electrode collector after recharging one or more times, causingthe coefficient of extension until fracturing in the coiling directionto be equal to or greater than 3% has been proposed (for example, referto Japanese Unexamined Patent Application Publication No. 2006-134762).

Further, out of an outer surface positive electrode active materiallayer and an inner surface positive electrode active material layer thatare provided on both sides of the positive electrode collector, causingthe thickness of the inner surface positive electrode active materiallayer to be less than the thickness of the outer surface electrodeactive material layer and providing an outer surface active materialregion in which only the outer surface active material layer is providedon a position that overlaps a lead on the coil center side of thepositive electrode has been proposed (for example, refer to JapaneseUnexamined Patent Application Publication No. 2008-004531). Out of aninner side positive electrode active material layer and an outer sidepositive electrode active material layer that are provided on thepositive electrode body, causing the center angle of an end portion on acoil center side of the outer side positive electrode active materiallayer and an end portion on a coil center side of the inner sidepositive electrode active material layer to the coil center to be equalto or greater than 72° and providing a positive electrode lead so as toavoid a region in which the center angle from the end portion of thecoil center side of the inner side positive electrode active materiallayer to be within 30° in the coil direction and within 30° in theopposite direction to the coil direction has been proposed (for example,refer to Japanese Unexamined Patent Application Publication No.2006-134763). Providing an outer circumference side opposing region inwhich the negative electrode active material layer and the positiveelectrode active material layer are opposing in only the outercircumference surface side to be within a range of equal to or more than2 revolutions and equal to or less than 3.25 revolutions on the coilcenter side of the negative electrode has been proposed (for example,refer to Japanese Unexamined Patent Application Publication No.2006-024464).

SUMMARY

Although a variety of measures and the like have been proposed tosuppress the fracturing of the positive electrode when coiling, there iscause, naturally, to not only suppress the fracturing of the positiveelectrode but to also secure the battery characteristics such as thebattery capacity or the cycle characteristics. The reason is that evenif fracturing of the positive electrode is able to be suppressed, if theusual performance of the battery is lowered, it is difficult to meet thedemand for further improvements in the performance of secondarybatteries. In particular, in order to realize higher capacity, beingable to suppress fracturing of the positive electrode even when theouter diameter of the coil core rod is reduced and the volume occupiedby the positive electrode and the negative electrode within thesecondary battery is increased while the thickness of the positiveelectrode collector is reduced and the thickness of the positiveelectrode active material layer is relatively increased is ideal.

Here, as described above, including a binder (copolymer) in the positiveelectrode active material layer has already been proposed. However, insuch a case, although fracturing of the positive electrode is suppressedsince the flexibility of the positive electrode active material layerincreases, since the adhesiveness of the positive electrode active layerto the positive electrode collector is reduced if the thickness of thepositive electrode active material layer is increased, the positiveelectrode active material layer becomes prone to fall off from thepositive electrode collector. On the other hand, if the addition amountof the binder is increased in order to improve the adhesiveness, sincethe flexibility of the positive electrode active material layer isdecreased, fracturing of the positive electrode is caused.

It is desirable to provide a secondary battery that is able to obtainexcellent battery characteristics while suppressing fracturing of apositive electrode when coiling, and a battery pack, an electronicapparatus, an electric tool, and electric vehicle, and a power storagesystem.

A secondary battery of an embodiment includes a spirally wound electrodebody in which a positive electrode and a negative electrode arelaminated via a separator and spirally wound with a center openingportion of the spirally wound electrode body as the center so that thepositive electrode is arranged more to an inner circumference side thanthe negative electrode. The positive electrode includes an innercircumference side positive electrode active material layer and an outercircumference side positive electrode active material layer. Further,the positive electrode includes a single side active material layerformation region in which only the outer circumference side positiveelectrode active material layer is formed on the positive electrodecollector on an end portion of an inner circumference side in an activematerial layer formation region in which the inner circumference sidepositive electrode active material layer and the outer circumferenceside positive electrode active material layer are formed. The ratioA/(A+B) of an area density A (mg/cm²) of the inner circumference sidepositive electrode active material layer and an area density B (mg/cm²)of the outer circumference side positive electrode active materiallayer, an inner diameter C (mm) of the coil opening portion, and theratio D/E of a thickness D (μm) of the positive electrode and athickness E (μm) of the positive electrode collector satisfy therelationship expressed in Formula 1 below. Further, a length F (mm) ofthe single side active material layer formation region satisfies therelationship expressed in Formula 2 below. Here, a battery pack, anelectronic apparatus, an electric tool, an electric vehicle, and a powerstorage system of embodiments of the disclosure use the secondarybattery described above.

0.380≦A/(A+B)≦[0.593−0.007×(D/E)]×(0.03×C+0.87)  (Formula 1)

-   -   (wherein C is 2.5≦C≦4 and D/E is 13.333≦D/E≦20)

[0.3×(D/E)²−7×(D/E)+45]≦F≦50  (Formula 2)

According to the secondary battery of the embodiment, the ratio A/(A+B)of the area density A of the inner circumference side positive electrodeactive material layer and the area density B of the outer circumferenceside positive electrode active material layer, the inner diameter of thecoil opening portion C, the ratio D/E of the thickness D of the positiveelectrode and the thickness E of the positive electrode collector, andthe length F of the single side active material formation region satisfythe relationships shown in Formulae 1 and 2. In such a case, therelationship between the area densities A and B in the relationship withthe inner diameter C and the thicknesses D and E is optimized, and thelength F in the relationship between the thicknesses D and E isoptimized Therefore, even when the inner diameter C is decreased (C=2.5mm to 4 mm) in order to increase the volume occupied by the positiveelectrode within the secondary battery and the ratio D/E is increased(D/E=13.333 to 20) in order to increase the volume occupied by the innercircumference side positive electrode active material layer and theouter circumference side positive electrode active material layer withinthe positive electrode, the positive electrode is not easily fracturedwhen coiling and battery capacity and cycle characteristics are secured.It is therefore possible to obtain excellent battery characteristicswhile suppressing fracturing of the positive electrode when coiling.Further, the same effects are able to be obtained by the battery pack,the electronic apparatus, the electric tool, the electric vehicle, andthe power storage system of the embodiments of the disclosure which usethe secondary battery described above.

Additional features and advantages are described herein, and will beapparent from the following Detailed Description and the figures.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a cross-sectional diagram that represents a configuration of asecondary battery of an embodiment;

FIG. 2 is a cross-sectional diagram along line II-II of the spirallywound electrode body illustrated in FIG. 1;

FIG. 3 is a cross-sectional diagram that represents a portion of thespirally wound electrode body illustrated in FIGS. 1 and 2;

FIGS. 4A and 4B are cross-sectional diagrams that represent a portion ofa positive electrode and a negative electrode illustrated in FIGS. 1 and2; and

FIG. 5 is a diagram that represents an analysis result of aSnCoC-containing material by XPS.

DETAILED DESCRIPTION

The present application will be described below with reference to thedrawings according to an embodiment.

<1. Secondary Battery>

FIGS. 1 to 4B represent a configuration of a secondary battery accordingto an embodiment. Of such diagrams, respectively, FIG. 1 illustrates anoverall vertical cross-section, FIG. 2 illustrates a horizontalcross-section along line II-II of a spirally wound electrode bodyillustrated in FIG. 1, and FIG. 3 illustrates a cross-section of aportion of the spirally wound electrode body 10 illustrated in FIG. 2.Further, FIGS. 4A and 4B illustrate cross-sections of a portion of anegative electrode 30 (A) and a positive electrode 20 (B) illustrated inFIGS. 2 and 3.

The secondary battery described here is a lithium ion secondary batteryin which the capacity of the negative electrode 30 is represented, forexample, by the absorption and discharge of lithium that is an electrodereactant.

[Overall Configuration of Secondary Battery]

In such a secondary battery, as illustrated in FIG. 1, mainly, thespirally wound electrode body 10 and a pair of insulating plates 2 and 3are stored inside a cylindrical battery casing 1. The battery shape thatuses such a cylindrical battery casing 1 is known as a cylinder type.

The battery casing 1 is an external casing with a hollow structure inwhich one end portion is sealed while the other end portion is open, andis formed of a metallic material such as iron (Fe), aluminum (Al), or analloy thereof. Here, in a case when the battery casing 1 is made ofiron, the surface of the battery casing 1 may be plated by a metallicmaterial such as nickel (Ni). The pair of insulating plates 2 and 3 arearranged so as to interpose the spirally wound electrode body 10 fromabove and below while extending vertically with respect to the coilcircumference surface.

A battery lid 4, a safety valve mechanism 5, and a heat-sensitiveresistance element (Positive Temperature Coefficient: PTC element) 6 arecaulked via a gasket 7 in the opened end portion of the battery casing1. The inside of the battery casing 1 is thereby sealed. The battery lid4 is formed, for example, of the same material as the battery casing 1.The safety valve mechanism 5 and the heat-sensitive resistance element 6are provided on the inner side of the battery lid 4, and the safetyvalve mechanism 5 is electrically connected to the battery lid 4 via theheat-sensitive resistance element 6. With the safety valve mechanism 5,if the internal pressure reaches a certain level or higher due tointernal short-circuiting or heating from the outside, a disk plate 5Ainverts and severs the electrical connection between the battery lid 4and the spirally wound electrode body 10. The heat-sensitive resistanceelement 6 has a function of preventing abnormal heating due to a largecurrent by using the increases in resistance corresponding to rises intemperature. The gasket 7 is formed, for example, of an insulatingmaterial, and asphalt may be applied on the surface thereof.

As illustrated in FIGS. 2 to 4B, the spirally wound electrode body 10includes a positive electrode 20, a negative electrode 30, and aseparator 41. The positive electrode 20 and the negative electrode 30are laminated via the separator 41 and the laminated body is spirallywound with a coil opening portion 50 (inner diameter C: mm) as thecenter so that the positive electrode 20 is arranged more on the innercircumference side than the negative electrode 30. Here, the number ofcoils is able to be set arbitrarily. The coil opening portion 50 is acylindrical space that is formed in the central portion of the coilelectrode body 10, and a center pin 51 may be inserted in the coilopening portion 50. The outer diameter of the center pin 51 isapproximately equal to the inner diameter C of the coil center portion50.

Here, for example, the spirally wound electrode body 10 further includesan auxiliary separator 42, and the positive electrode 20, the separator41, the negative electrode 30, and the auxiliary separator 42 arelaminated and spirally wound to be arranged in such an order from theinner circumference side. Here, the outer diameter of the spirally woundelectrode body 10 is, for example, equal to or greater than 12.8 mm andequal to or less than 18.4 mm.

A positive electrode lead 8 formed of a conductive material such asaluminum, for example, is connected to the positive electrode 20, andthe positive electrode lead 8 is welded to the safety valve mechanism 5and electrically connected to the battery lid 4. Further, a negativeelectrode lead 9 formed of a conductive material such as nickel, forexample, is connected to the negative electrode 30, and the negativeelectrode lead 9 is welded to the battery casing 1.

[Positive Electrode]

As illustrated in FIGS. 2 to 4B, the positive electrode 20 (thickness D:μm) respectively has an inner circumference side positive electrodeactive material layer 22 (area density A: mg/cm²) and an outercircumference side positive electrode active material layer 23 (areadensity B: mg/cm²) on an inner circumference side surface and an outercircumference side surface of a strip-like positive electrode collector21 (thickness E: μm). The inner circumference side surface is onesurface that is positioned on the inner circumference side of the pairof opposing surfaces of the positive electrode collector 21, and theouter circumference side surface is the other surface that is positionedon the outer circumference side. Here, the thickness D is, for example,equal to or greater than 200 μm and equal to or less than 300 μm.

The positive electrode collector 21 is formed of a conductive materialsuch as, for example, aluminum, nickel, or stainless steel. The innercircumference side positive electrode active material layer 22 and theouter circumference side positive electrode active material layer 23include one or more of a positive electrode material that is able toabsorb and discharge lithium as the positive electrode active material,and may also include other materials such as a positive electrode binderor a positive electrode conductive agent as necessary. Here, thethickness E is, for example, equal to or greater than 12 μm and equal toor less than 20 μm. The area density A is, for example, equal to orgreater than 26 mg/cm² and equal to or less than 51 mg/cm², and the areadensity B is, for example, equal to or greater than 26 mg/cm² and equalto or less than 72 mg/cm².

The inner circumference side positive electrode active material layer 22and the outer circumference side positive electrode active materiallayer 23 are formed, for example, on a central portion (active materiallayer formation region 20X) in the longitudinal direction of thepositive electrode collector 21 to be opposing one another via thepositive electrode collector 21. On the other hand, in an end portionregion (inactive material layer formation region 20Y) where the innercircumference side positive electrode active material layer 22 and theouter circumference side positive electrode active material layer 23 arenot formed, the positive electrode collector 21 is exposed. However, thepositive electrode 20 includes a single side active material layerformation region 20Z (length F: mm) on which only the outercircumference side positive electrode active material layer 23 is formedon the positive electrode collector 21 on an end portion of the innercircumference side of the active material layer formation region 20X.

The positive electrode collector 21 in the inactive material layerformation region 20Y may, for example, be spirally wound by onerevolution or two or more revolutions along with the separator 41 andthe auxiliary separator 42 around one or both of the inner circumferenceside and the outer circumference side. Here, the positions of the endportions on the outer circumference side of the inner circumference sidepositive electrode active material layer 22 and the outer circumferenceside positive electrode active material layer 23, for example, matcheach other in the longitudinal direction of the positive electrodecollector 21. However, the positions of the end portions may bedeviated.

A lithium-containing compound is preferable as the positive electrodematerial. The reason is that it is then possible to obtain a high energydensity. The lithium-containing compound is, for example, a compositeoxide that includes lithium and a transition metal element asconstituent elements, a phosphate compound that includes lithium and atransition metal element as constituent elements, or the like. Amongsuch materials, a material that includes at least one of cobalt (Co),nickel (Ni), manganese (Mn), and iron (Fe) as the transition metalelement is preferable. The reason is that a higher voltage is therebyobtained. The chemical formula thereof is expressed, for example, asLi_(x)MLO₂ or Li_(y)M2PO₄. M1 and M2 in the formulae represent the oneor more transition metal elements. Although the values of x and y aredifferent depending on the charging and discharging state, the values ofx and y are usually 0.05≦x≦1.10 and 0.05≦y≦1.10.

The composite oxide that includes the lithium and the transition metalelement is, for example, a lithium cobalt composite oxide (Li_(x)CoO₂),a lithium nickel composite oxide (Li_(x)NiO₂), the lithium nickelcomposite oxide series expressed in Formula 10, or the like. Thephosphate compound that includes the lithium and the transition metalelement is, for example, a lithium iron phosphate compound (LiFePO₄), alithium iron manganese phosphate compound (LiFe_(1−u)Mn_(u)PO₄(u<1)), orthe like. The reason is that it is thereby possible to obtain a highbattery capacity and to obtain excellent cycle characteristics. Here,the positive electrode material may be a material other than thosedescribed above. The material expressed by Li_(x)M1_(y)O₂ (M1 is atleast one of nickel and the M expressed in Formula 1 (all metal elementsincluding nickel and M), x is x>1, and y is arbitrary) or the like is anexample.

LiNi_(1−x)M_(x)O₂  (Formula 10)

(M is at least one of cobalt, manganese, iron, aluminum, vanadium (V),tin (Sn), magnesium (Mg), titanium (Ti), strontium (Sr), calcium (Ca),zirconium (Zr), molybdenum (Mo), technetium (Tc), ruthenium (Ru),tantalum (Ta), tungsten (W), rhenium (Re), ytterbium (Yb), copper (Cu),zinc (Zn), barium (Ba), boron (B), chromium (Cr), silicon (Si), gallium(Ga), phosphorous (P), antimony (Sb), and niobium (Nb). x is0.005<x<0.5.)

Otherwise, the positive electrode material may, for example, be anoxide, a disulfide, a chalcogenide, a conductive polymer, or the like.The oxide is, for example, titanium oxide, vanadium oxide, or manganesedioxide. The disulfide is, for example, titanium disulfide, molybdenumsulfide, or the like. The chalcogenide is, for example, niobium selenideor the like. The conductive polymer is, for example, sulfur,polyaniline, polythiophene, or the like.

The inner circumference side positive electrode active material layer 22and the outer circumference side positive electrode active materiallayer 23 are formed, for example, by an application method, acalcination method (sintering method), or a method of using both. Theapplication method is, for example, a method of applying by mixing aparticle-like positive electrode active material with a positiveelectrode binder or the like and dispersing in an organic solvent or thelike. The calcination method is, for example, a method of applying bythe same procedures as in the application method before heating by atemperature that is higher than the melting point of the positiveelectrode binder or the like. As the calcination method, a commontechnique may be used. For example, an atmosphere calcination method, areaction calcination method, or a hot press calcination method may beused.

The positive electrode binder is, for example, one or more of asynthetic rubber, a polymer material, or the like. The synthetic rubberis, for example, styrene-butadiene rubber, fluorinated rubber, ethylenepropylene diene, or the like. The polymer material is, for example,polyvinylidene fluoride, polyimide, polyamideimide, polyacrylic acid, orlithium polyacrylate, or the like. Here, the mixing ratio of thepositive electrode binder with respect to the positive electrode activematerial is, for example, equal to or greater than 2% and equal to orless than 5% by mass (equal to or greater than 2 parts and equal to orless than 5 parts of the positive electrode binder to 100 parts of thepositive electrode active material). The reason is that if the ratio isless than 2%, the adhesion of the inner circumference side positiveelectrode active material layer 22 and the outer circumference sidepositive electrode active material layer 23 with respect to the positiveelectrode collector 21 decreases, and on the other hand, if the ratio isgreater than 5%, there is a possibility of the energy densitydecreasing.

The positive electrode conductive agent is one or more of, for example,carbon materials such as graphite, carbon black, acetylene black, orketjen black. Here, as long as the negative electrode conductive agentis a material with conductivity, the negative electrode conductive agentmay be a metallic material, a conductive polymer, or the like.

Here, the ratio A/(A+B) of the area density A of the inner circumferenceside positive electrode active material layer 22 and the area density Bof the outer circumference side positive electrode active material layer23, the inner diameter C of the coil opening portion 50, and the ratioD/E of the thickness D of the positive electrode 20 and the thickness Eof the positive electrode collector 21 satisfy the relationshipexpressed in Formula 1 below. Further, the length F of the single sideactive material layer region 20Z satisfies the relationship expressed inFormula 2 below. Here, the ratio A/(A+B) and the ratio D/E are bothvalues that are rounded to the fourth decimal place, and the length F isa value that is rounded to the second decimal place.

0.380≦A/(A+B)≦[0.593−0.007×(D/E)]×(0.03×C+0.87)  (Formula 1)

-   -   (wherein C is 2.5≦C≦4 and D/E is 13.333≦D/E≦20)

[0.3×(D/E)²−7×(D/E)+45]≦F≦50  (Formula 2)

The ratio A/(A+B) satisfies the relationship expressed in Formula 1because since the relationship between the area densities A and B in therelationship between the inner diameter C and the thicknesses D isoptimized, upon the creation process of the spirally wound electrodebody 10, fracturing of the positive electrode 20 is suppressed whencoiling and battery capacity and cycle characteristics are secured.

In detail, if the ratio A/(A+B) is small, since the absolute amount ofthe inner circumference side positive electrode active material layer 22that is positioned on a side near the coil opening portion 50 decreasesrelative to the absolute amount of the outer circumference side positiveelectrode active material layer 23, there is a tendency that thepositive electrode 20 does not easily fracture when coiling. However, ifthe ratio A/(A+B) is too small, since the balance between the absoluteamount of the inner circumference side positive electrode activematerial layer 22 and the absolute amount of the outer circumferenceside positive electrode active material layer 23 deteriorates, ifcharging and discharging is repeated as the discharging capacitydecreases, the discharging capacity decreases more easily. On the otherhand, if the ratio A/(A+B) is too great, since the absolute amount ofthe inner circumference side positive electrode active material layer 22increases relative to the absolute amount of the outer circumferenceside positive electrode active material layer 23, the positive electrode20 becomes prone to fracturing when coiling. However, if the ratioA/(A+B) satisfies the relationship expressed in Formula 1, the ratioA/(A+B) is optimized from the point of view of suppressing fracturing ofthe positive electrode 20 and a decrease in the discharge capacity.Therefore, even when the thickness D is increased relative to thethickness E and the volume occupied by the inner circumference sidepositive electrode active material layer 22 and the outer circumferenceside positive electrode active material layer 23 within the secondarybattery is increased, the electrode 20 does not easily fracture duringcoiling. Such a tendency of the positive electrode 20 becoming resistantto fracturing may be similarly obtained when, in particular, the innerdiameter C is reduced and the radius of curvature of the positiveelectrode 20 that is spirally wound in the vicinity of the coil openingportion 50 is reduced. Moreover, since the area density A is less thanthe area density B and both the area densities A and B are sufficient, ahigh discharging capacity is obtained and the discharging capacity doesnot easily decrease even when charging and discharging is repeated.

Here, the inner diameter C is within the range described above in orderto reduce the volume occupied by the coil opening portion 50, whichrepresents a loss of space, within the secondary battery, and toincrease the volume occupied by the positive electrode 20 and thenegative electrode 30. Further, the ratio D/E is within the rangedescribed above in order to increase the thickness D relative to thethickness E and to increase the volume occupied by the innercircumference side positive electrode active material layer 22 and theouter circumference side positive electrode active material layer 23within the positive electrode 20.

The length F satisfies the relationship expressed in Formula 2 becausesince the length F is optimized in the relationship between thethicknesses D and E, fracturing of the positive electrode 20 issuppressed when coiling and battery capacity and cycle characteristicsare secured.

In detail, if the length F is too short, since there is too much of theinner circumference side positive electrode active material layer 22 inthe vicinity of the coil opening portion 50 where the radius ofcurvature when coiling is the smallest, the positive electrode 20 isprone to fracturing. On the other hand, if the length F is too long,since the range within which the inner circumference side positiveelectrode active material layer 22 is reduced too much, the batterycapacity is reduced. However, if the length F satisfies the relationshipexpressed in Formula 2, since the length F is optimized from theviewpoints of suppressing fracturing of the positive electrode 20 andsecuring battery capacity, even if the thickness D is increased relativeto the thickness E, the positive electrode 20 does not easily fracturewhen coiling and a high discharging capacity is maintained.

In particular, the length F preferable satisfies the relationshipexpressed in Formula 3 below. The reason is that the cyclecharacteristics are then improved.

0.428≦A/(A+B)[0.593−0.007×(D/E)]×(0.03×C+0.87)  (Formula 3)

[Negative Electrode]

As illustrated in FIGS. 2 to 4B, for example, the negative electrode 30respectively includes an inner circumference side negative electrodeactive material layer 32 and an outer circumference side negativeelectrode active material layer 33 on an inner circumference sidesurface and an outer circumference side surface of a strip-like negativeelectrode collector 31. Here, the thickness of the negative electrode 30is, for example, equal to or greater than 66 μm and equal to or lessthan 123 μm.

The negative electrode collector 31 is formed of a conductive materialsuch as, for example, copper, nickel, or stainless steel. The innercircumference side negative electrode active material layer 32 and theouter circumference side negative electrode active material layer 33include one or more of a negative electrode material that is able toabsorb and discharge lithium as the negative electrode active material,and may also include other materials such as a negative electrode binderor a negative electrode conductive agent as necessary. It is preferablethat the dischargeable capacity of the negative electrode material begreater than the discharging capacity of the positive electrode 20 inorder to suppress separating of the lithium metal when discharging.Here, the details relating to the negative electrode binder or thenegative electrode conductive agent, for example, are respectively thesame as those of the positive electrode binder and the positiveelectrode conductive agent. Here, the thickness of the negativeelectrode collector 31 is, for example, equal to or greater than 12 μmand equal to or less than 20 μm. The area density of the innercircumference side negative electrode active material layer 32 is, forexample, equal to or greater than 7 mg/cm² and equal to or less than 13mg/cm², and the area density of the outer circumference side negativeelectrode active material layer 33 is, for example, equal to or greaterthan 7 mg/cm² and equal to or less than 19 mg/cm². The mixing ratio ofthe negative electrode binder to the negative electrode active materialis, for example, the same as the mixing ratio of the positive electrodebinder to the positive electrode active material.

The inner circumference side negative electrode active material layer 32and the outer circumference side negative electrode active materiallayer 33 are formed, for example, on a central portion (active materiallayer formation region 30X) in the longitudinal direction of thenegative electrode collector 31 to be opposing one another via thenegative electrode collector 31. On the other hand, in an end portionregion (inactive material layer formation region 30Y) where the innercircumference side negative electrode active material layer 32 and theouter circumference side negative electrode active material layer 33 arenot formed, the negative electrode collector 31 is exposed. It ispreferable that the length of the active material layer formation region30X (formation lengths of the inner circumference side negativeelectrode active material layer 32 and the outer circumference sidenegative electrode active material layer 33) be, for example, greaterthan the length of the active material layer formation region 20X(formation lengths of the inner circumference side positive electrodeactive material layer 22 and the outer circumference side positiveelectrode active material layer 23) in both the outer circumference sideand the inner circumference side.

The negative electrode collector 31 in the inactive material layerformation region 30Y may, for example, be spirally wound by onerevolution or more revolutions along with the separator 41 and theauxiliary separator 42 around one or both of the inner circumferenceside and the outer circumference side. Here, the positions of the endportions on the outer circumference side of the inner circumference sidenegative electrode active material layer 32 and the outer circumferenceside negative electrode active material layer 33 match the other and thepositions of the end portions on the inner circumference side match theother in the longitudinal direction of the negative electrode collector31. However, the positions of the end portions may be deviated.

It is preferable that the surface of the negative electrode collector 31be roughened. The reason is that, due to the so-called anchor effect,the adhesiveness of the inner circumference side negative electrodeactive material layer 32 and the outer circumference side negativeelectrode active material layer 33 to the negative electrode collector31 improves. In such a case, the surface of the negative electrodecollector 31 may be roughened in at least a region that opposes theinner circumference side negative electrode active material layer 32 andthe outer circumference side negative electrode active material layer33. For example, there is a method of forming microparticles by anelectrolysis process. The electrolysis process is a method of providingconvexities and concavities by forming microparticles on the surface ofthe negative electrode collector 31 by electrolysis in an electrolysistank. Copper foil that is created by an electrolytic method is generallyreferred to an electrolytic copper foil.

The negative electrode material is, for example, a carbon material. Thereason is that since there is very little change in the crystallinestructure when the lithium is absorbed and discharged, a high energydensity and excellent cycle characteristics are able to be obtained.Further, it is because a carbon material also functions as the negativeelectrode conductive agent. The carbon material is, for example,graphatizable carbon, non-graphatizable carbon in which the surfaceinterval of (002) surface is equal to or greater than 0.37 nm, orgraphite in which the surface interval of (002) surface is equal to orless than 0.34 nm More specifically, the carbon material is pyrolyticcarbon, coke, a glassy carbon fiber, an organic polymer compound fiber,activated carbon, or carbon black. Among such materials, coke includespitch coke, needle coke, and petroleum coke. The organic polymercompound fiber is a material in which a phenol resin, a furan resin, orthe like is carbonized by being calcined at an appropriate temperature.Otherwise, the carbon material may be low-crystalline carbon oramorphous carbon that have been heated by approximately 1000° C. orlower. Here, the form of the carbon material may be any of a fiber form,a spherical form, a grain form, or a scaled form.

Further, it is preferable that a material (metallic material) includeone or more of a metallic element or a semi-metallic element as aconstituent element of the negative electrode material. The reason isthat a high energy density is thereby obtained. The metallic materialmay be a single element, an alloy, or a compound of a metallic elementor a semi-metallic element, may be two or more types thereof, or amaterial that includes at least one or more of phases thereof as aportion thereof. Here, an alloy in the embodiments of the disclosureincludes, in addition to a material that includes two or more types ofmetallic elements, a material that includes one or more types ofmetallic elements and one or more types of semi-metallic elements.Further, an alloy may include a non-metallic element. The structure ofan alloy is a solid solution, a eutectic system (eutectic mixture), anintermetallic compound, a coexistence of two or more types thereof, orthe like.

The metallic element or the semi-metallic element is, for example, ametallic element or a semi-metallic element that is able to form analloy with lithium, and specifically, is one or more of the elementsbelow. Such elements are magnesium (Mg), boron (B), aluminum (Al),gallium (Ga), indium (In), silicon (Si), germanium (Ge), tin (Sn), orlead (Pb). Furthermore, the materials are bismuth (Bi), cadmium (Cd),silver (Ag), zinc, hafnium (Hf), zirconium (Zr), yttrium (Y), palladium(Pd), or platinum (Pt). Among such materials, at least one of siliconand tin are preferable. The reason is that since silicon and tin haveexcellent abilities of absorbing and discharging lithium, a high energydensity is obtained.

A material that includes at least one of silicon and tin may be a singleelement, an alloy, or a compound of silicon or tin, may be two or moretypes thereof, or a material that includes at least one or more ofphases thereof as a portion thereof. Here, a single element is a singleelement in a general sense (may include miniscule amounts ofimpurities), and does not necessarily mean a purity of 100%.

An alloy of silicon is a material that includes, for example, as aconstituent element other than silicon, one or more of the elementsbelow. Such elements are tin, nickel, copper, iron, cobalt, manganese,zinc, indium, silver, titanium, germanium, bismuth, antimony, orchromium. A compound of silicon is a material that includes, forexample, as a constituent element other than silicon, oxygen or carbon.Here, a compound of silicon may include, for example, as a constituentelement other than silicon, one or more of any of the elements describedfor an alloy of silicon.

The materials below are specific examples of alloys or compounds ofsilicon. Such materials are SiB₄, SiB₆, Mg₂Si, Ni₂Si, TiSi₂, MoSi₂,CoSi₂, NiSi₂, CaSi₂, CrSi₂, Cu₅Si, FeSi₂, MnSi₂, NbSi₂, or TaSi₂.Further, such materials are VSi₂, WSi₂, ZnSi₂, SiC, Si₃N₄, Si₂N₂O,SiO_(v) (0v≦2), or LiSiO. Here, v in SiO_(v) may be 0.2<v<1.4.

An alloy of tin is a material that includes, for example, as aconstituent element other than tin, one or more of the elements below.Such elements are silicon, nickel, copper, iron, cobalt, manganese,zinc, indium, silver, titanium, germanium, bismuth, antimony, orchromium. A compound of tin is a material that includes, for example, asa constituent element other than tin, oxygen or carbon. Here, a compoundof tin may include, for example, as a constituent element other thantin, one or more of any of the elements described for an alloy of tin.As an alloy or compound of tin, SnO_(w) (0<w≦2), SnSiO₃, LiSnO, or Mg₂Snare given as examples.

In particular, a material that includes tin as a constituent element is,for example, preferably a material that includes tin as a firstconstituent element, and second and third constituent elements inaddition. The second constituent element is, for example, one or more ofany of the elements below. Such materials are cobalt, iron, magnesium,titanium, vanadium, chromium, manganese, nickel, copper, zinc, gallium,or zirconium. Further, such materials are niobium, molybdenum, silver,indium, cerium, hafnium, tantalum, tungsten, bismuth, or silicon. Thethird constituent element is, for example, one or more of boron, carbon,aluminum, or phosphorous. The reason is that by including the second andthird constituent elements, a high battery capacity and excellent cyclecharacteristics are obtained.

Among such materials, a material that includes tin, cobalt, and carbon(SnCoC-containing material) is preferable. The composition of theSnCoC-containing material is, for example, 9.9 mass % to 29.7 mass % ofthe carbon content and the proportion of the content of the tin and thecobalt (Co/(Sn+Co)) is 20 mass % to 70 mass %. The reason is that a highenergy density is obtained within such a composition range.

The SnCoC-containing material includes a phase containing tin, cobalt,and carbon, and the phase is preferably low-crystalline or amorphous.The phase is a reaction phase that is able to react with lithium, andexcellent characteristics are obtained due to the presence of such aphase. The half-value width of the diffraction peak that is obtained byan X-ray diffraction of the phase preferably has, in a case when CuKalpha rays are used as specified X-rays and the insertion speed is1°/min, a diffraction angle 2θ of equal to or greater than 1°. Thereason is that the lithium is then absorbed and discharged more smoothlyand the reactivity with the electrolyte solution is reduced. Here, theremay be a case when the SnCoC-containing material includes, in additionto the low-crystalline or amorphous phase, a phase that includes asingle element or a portion of each constituent element.

Whether or not the diffraction peak that is obtained by X-raydiffraction corresponds to a reaction phase that is able to react withlithium is easily determined by comparing the X-ray diffraction chartbefore and after an electrochemical reaction with the lithium. Forexample, if the position of the diffraction peak changes before andafter the electrochemical reaction with the lithium, the diffractionpeak corresponds to a reaction phase that is able to react with thelithium. In such a case, for example, the diffraction peak of thelow-crystalline or amorphous reaction phase is seen between 2θ=20° to50°. Such a reaction phase includes, for example, each of theconstituent elements described above, and is mainly low-crystalline oramorphous due to the presence of carbon.

The SnCoC-containing material is preferably bound with a metallicelement or a semi-metallic element in which at least a portion of thecarbon that is a constituent element is another constituent element. Thereason is that aggregation or crystallization of tin or the like is thensuppressed. The bonding state of an element is able to be verified, forexample, by an X-ray photoelectron spectroscopy (XPS) method. In acommercially available device, for example, an Al—K alpha ray, Mg—Kalpha ray, or the like is used as a soft X-ray. In a case when at leasta portion of the carbon is bound with a metallic element, asemi-metallic element, or the like, the peak of the synthetic wave of a1s trajectory of the carbon (C1s) appears in a region that is lower than284.5 eV. Here, energy calibration is performed so that the peak of a 4f trajectory of a gold atom (Au4f) is obtained at 84.0 eV. At this time,ordinarily, since there is surface contamination carbon on the materialsurface, the peak of C1s of the surface contamination carbon is 284.8eV, which is used as the energy reference. In an XPS measurement, sincethe waveform of the peak of C1s is obtained in a form that includes thepeak of the surface contamination carbon and the peak of the carbonwithin the SnCoC-containing material, for example, analysis is performedusing commercially available software and the peak of each is separated.In the analysis of the waveform, the position of the main peak that ispresent on a minimum binding energy side is the energy reference (284.8eV).

Here, the SnCoC-containing material may include other constituentelements as necessary. As such other constituent elements, one or moreof silicon, iron, chromium, indium, niobium, germanium, titanium,molybdenum, aluminum, phosphorous, gallium, and bismuth are exemplified.

Other than such SnCoC-containing materials, a material that containstin, cobalt, iron, and carbon (SnCoFeC-containing material) is alsopreferable. The composition of the SnCoFeC-containing material is ableto be set arbitrarily. For example, the composition in a case whensetting such that the content of the iron is relatively small is asbelow. The content of the carbon is between 9.9 mass % and 29.7 mass %,the content of the iron is between 0.3 mass % and 5.9 mass %, and theproportion of the content of the tin and the cobalt (Co/(Sn+Co)) isbetween 30 mass % and 70 mass %. Further, for example, the compositionin a case when setting such that the content of the iron is relativelylarge is as below. The content of the carbon is between 11.9 mass % and29.7 mass %. Further, the proportion of the content of the tin, thecobalt, and the iron ((Co+Fe)/(Sn+Co+Fe)) is between 26.4 mass % and48.5 mass %, and the proportion of the content of the cobalt and theiron (Co/(Co+Fe)) is between 9.9 mass % and 79.5%. The reason is that ahigh energy density is obtained with such a composition range. Theproperties (half-value width and the like) of the SnCoFeC-containingmaterial are the same as those of the SnCoC-containing materialdescribed above.

Otherwise, the negative electrode material may, for example, be a metaloxide or a polymer compound. A metal oxide is, for example, iron oxide,ruthenium oxide, molybdenum oxide, or the like. A polymer compound is,for example, polyacetylene, polyaniline, polypyrrole, or the like.

The negative electrode may be, naturally, materials other than thosedescribed above. Further, two or more types of the series of negativeelectrode materials described above may be mixed in arbitrarycombinations.

The inner circumference side negative electrode active material layer 32and the outer circumference side negative electrode active materiallayer 33 are formed, for example, by an application method, a vapormethod, a liquid method, a spraying method, a calcining method, or twoor more types thereof. The vapor method is, for example, a physicaldeposition method or a chemical deposition method, and specifically, isa vacuum vapor deposition method, a sputtering method, an ion platingmethod, a laser ablation method, a thermo-chemical vapor depositionmethod, a chemical vapor deposition (CVD) method, a plasma chemicalvapor deposition method, or the like. The liquid method is, for example,an electrolytic plating method, an electroless plating method, or thelike. The spraying method is a method of spraying the negative electrodeactive material in a molten or semi-molten state.

[Separator]

The separator 41 and the auxiliary separator 42 allow lithium ions topass through while separating the positive electrode 20 and the negativeelectrode 30 and preventing the shirt-circuiting of electrical currentsdue to contact between the electrodes. The separator 41 and theauxiliary separator 42 may, for example, porous membranes of a syntheticresin, a ceramic, or the like, and may be a laminate of two or moretypes of such porous membranes. The synthetic resin is, for example,polytetrafluoroethylene, polypropylene, polyethylene terephthalate,polyethylene, or the like. Here, the thicknesses of the separator 41 andthe auxiliary separator 42 are, for example, equal to or greater than 16μm and equal to or less than 20 μm.

The separator 41 and the auxiliary separator 42 may coil around one orboth of the inner circumference side and the outer circumference side ofthe spirally wound electrode body 10 over one revolution or two or morerevolutions. However, the coiling state of the separator 41 and theauxiliary separator 42 on the outer circumference side is preferably setaccording to the type of electrode terminal for the battery casing 1 toperform a function. Specifically, in a case when the battery casing 1functions as the same terminal (negative electrode terminal) as theelectrode on the outer circumference side (negative electrode 30), inorder to deliberately bring the negative electrode 30 and the batterycasing 1 into contact in a case when a nail is struck in the secondarybattery or the like, it is preferable that the separator 41 and theauxiliary separator 42 be not spirally wound excessively beyond thenegative electrode collector 31 in the inactive material layer formationregion 30Y. On the other hand, in a case when the battery casing 1functions as a terminal that is a difference electrode (positiveelectrode) from the electrode on the outer circumference side (negativeelectrode 30), in order that the negative electrode 30 and the batterycasing 1 are not positively brought into contact, it is preferable thatthe separator 41 and the auxiliary separator 42 be spirally wound inexcess beyond the negative electrode collector 31 in the inactivematerial layer region 30Y.

[Electrolyte]

An electrolyte solution that is a liquid electrolyte is impregnated intothe separator 41 and the auxiliary separator 42. The electrolytesolution includes a solvent and an electrolytic salt, and may alsoinclude other materials such as various types of additives as necessary.

The solvent is, for example, one or more of any of the below non-aqueoussolvents (organic solvents). Such non-aqueous solvents are ethylenecarbonate, propylene carbonate, butylene carbonate, dimethyl carbonate,diethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate,γ-butyrolactone, γ-valerolactone, 1,2-dimethoxyethane, ortetrahydrofuran. Further, the non-aqueous solvent is2-methyltetrahydrofuran, tetrahydropyran, 1,3-dioxolane,4-methyl-1,3-dioxolane, 1,3-dioxane, or 1,4-dioxane. Further, thenon-aqueous solvent is methyl acetate, ethyl acetate, methyl propionate,ethyl propionate, methyl butyrate, methyl isobutyrate, methyl trimethylacetate, or ethyl trimethyl acetate. Further, the non-aqueous solvent isacetonitrile, glutaronitrile, adiponitrile, methoxyacetonitrile,3-methoxypropionile, N,N-dimethylformamide, N-methylpyrrolidone orN-methyl oxazolidinone. Further, the non-aqueous solvent isN,N′-dimethylimidazolidinone, nitromethane, nitroethane, sulfolane,trimethyl phosphate, or dimethylsulfoxide. The reason is that excellentbattery capacity, cycle characteristics, storage characteristics, andthe like are thus obtained.

Among such materials, at least one of ethylene carbonate, propylenecarbonate, dimethyl carbonate, diethyl carbonate, and ethyl methylcarbonate is preferable. The reason is that further superiorcharacteristics are thus obtained. In such a case, a combination of asolvent with a high viscosity (electric permittivity) such as ethylenecarbonate or propylene carbonate (for example, relative permittivityε≧30) and a solvent with a low viscosity such as dimethyl carbonate,ethyl methyl carbonate, or diethyl carbonate (for example, viscosity ≦1mPa·s) is preferable. The reason is that the dissociability of theelectrolytic salt and the mobility of ions are thus improved.

In particular, the solvent may be unsaturated carbon bond cyclic estercarbonate (cyclic ester carbonate including one or more unsaturatedcarbon bonds). The reason is that since a stable coating is formed onthe surface of the negative electrode 30 when charging and discharging,the decomposition reaction of the electrolyte solution is suppressed.The unsaturated carbon bond cyclic ester carbonate is, for example,vinylene carbonate, vinyl ethylene carbonate, or the like. Here, thecontent of the unsaturated carbon bond cyclic ester carbonate in anon-aqueous solvent is, for example, equal to or more than 0.01 mass %and equal to or less than 10 mass %. The reason is that thedecomposition reaction of the electrolyte solution is thus suppressedwithout excessively lowering the battery capacity.

Further, the solvent may be at least one of halogenated chained estercarbonate (chained ester carbonate with one or more halogen groups) orhalogenated cyclic ester carbonate (cyclic ester carbonate with one ormore halogen groups). The reason is that since a stable coating is thusformed on the surface of the negative electrode 30 when charging anddischarging, the decomposition reaction of the electrolyte solution issuppressed. Although the types of halogen groups are not particularlylimited, a fluorine group (—F), a chlorine group (—Cl), or a brominegroup (—Br) are preferable, and a fluorine group is more preferable. Thereason is that even greater effects are thus obtained. However, thenumber of halogen groups is preferably two rather than one, and may bethree or more. The reason is that since a stronger and more stablecoating is thus formed, the decomposition reaction of the electrolytesolution is further suppressed. The halogenated chained ester carbonateis, for example, fluoromethyl methyl carbonate, bis (fluoromethyl)carbonate, difluoromethyl methyl carbonate, or the like. The halogenatedcyclic ester carbonate is 4-fluoro-1,3-dioxolan-2-one,4,5-difluoro-1,3-dioxolan-2-one, or the like. Here, the content of thehalogenated chained ester carbonate and the halogenated cyclic estercarbonate in the non-aqueous solvent is, for example, equal to orgreater than 0.01 mass % and equal to or less than 50 mass %. The reasonis that it is thus possible suppress the decomposition reaction of theelectrolyte solution without excessively lowering the battery capacity.

Further, the solvent may be sultone (cyclic sulfonate). The reason isthat the chemical stability of the electrolyte solution is improved. Thesultone is, for example, propane sultone, propene sultone, or the like.Here, the content of the sultone within the non-aqueous solvent is, forexample, equal to or greater than 0.5 mass % and equal to or less than 5mass %. The reason is that it is thus possible suppress thedecomposition reaction of the electrolyte solution without excessivelylowering the battery capacity.

Furthermore, the solvent may be acid anhydride. The reason is that thechemical stability of the electrolyte solution is thus improved. Theacid anhydride is, for example, dicarboxylic anhydride, disulfonic acidanhydride, carbonate sulfonic acid anhydride, or the like. Thedicarboxylic anhydride is, for example, succinic anhydride, glutaricanhydride, maleic anhydride, or the like. The disulfonic acid anhydrideis, for example, ethane disulfonic anhydride, propane disulfonic acidanhydride, or the like. The carbonate sulfonic acid anhydride is, forexample, sulfobenzoic acid anhydride, sulfopropionic acid anhydride,sulfobutyric acid anhydride, or the like. Here, the content of the acidanhydride within the non-aqueous solution is, for example, equal to orgreater than 0.5 mass % and equal to or less than 5 mass %. The reasonis that it is thus possible to suppress the decomposition reaction ofthe electrolyte solution without excessively lowering the batterycapacity.

[Electrolytic Salt]

The electrolytic salt is, for example, one or more of the lithium saltsbelow. However, the electrolytic salt may be a salt other than lithiumsalt (for example, a light metal salt other than lithium salt).

The lithium salt is, for example, the compounds below. The lithium saltis lithium hexafluorophosphate (LiPF₆), lithium tetrafluoroborate(LiBF₄), lithium perchlorate (LiClO₄), or lithium hexafluoroarsenate(LiAsF₆). Further, the lithium salt is lithium tetraphenylborate(LiB(C₆H₅)₄), lithium methanesulfonate (LiCH₃SO₃), lithiumtrifluoromethanesulfonate (LiCF₃SO₃), or lithium tetrachloroaluminate(LiAlCl₄). Furthermore, the lithium salt is lithium hexafluorosilicate(Li₂SiF₆), lithium chloride (LiCl), or lithium bromide (LiBr). Thereason is that excellent battery capacity, cycle characteristics, andstorage characteristics are thus obtained.

At least one type out of the lithium hexafluorophosphate, lithiumtetrafluoroborate, lithium perchlorate, and lithium hexafluoroarsenateis preferable, and lithium hexafluorophosphate is more preferable. Thereason is that since internal resistance is thus reduced, even greatereffects are obtained.

The content of the electrolytic salt is preferably equal to or greaterthan 0.3 mol/kg and equal to or less than 3.0 mol/kg with respect to thesolvent. The reason is that high ion conductivity is thus obtained.

[Manufacturing Method of Secondary Battery]

The secondary battery is manufactured, for example, by the followingtechniques.

First, the positive electrode 20 is created. In such a case, aftermixing a positive electrode binder or a positive electrode conductiveagent as necessary with the positive electrode active material to createa positive electrode compound, the positive electrode compound isdispersed in an organic solvent or the like to form a paste-likepositive electrode compound slurry. Next, the positive electrodecompound slurry is applied on both surfaces of the positive electrodecollector 21 before being dried, and the inner circumference sidepositive electrode active material layer 22 and the outer circumferenceside positive electrode active material layer 23 are formed. Finally,the inner circumference side positive electrode active material layer 22and the outer circumference side positive electrode active materiallayer 23 are compression molded while being heated as necessary. Thearea densities A and B are adjustable by such compression molding. Insuch a case, the compression molding may be repeated a plurality oftimes.

Next, the negative electrode 30 is created by the same technique as thepositive electrode 20 described above. In such a case, a negativeelectrode compound in which a negative electrode binder, a negativeelectrode conductive agent, or the like is mixed as necessary isdispersed in an organic solvent or the like, and a paste-like negativeelectrode compound slurry is formed. Next, the negative electrodecompound slurry is applied on both surfaces A of the negative electrodecollector 31 before being dried, and after the inner circumference sidenegative electrode active material layer 32 and the outer circumferenceside negative electrode active material layer 33 are formed, the innercircumference side negative electrode active material layer 32 and theouter circumference side negative electrode active material layer 33 arecompression molded as necessary.

Here, the negative electrode 30 may be created by different techniquesfrom the positive electrode 20. In such a case, for example, thenegative electrode material is deposited on both surfaces of thenegative electrode collector 31 using an evaporation method or a vapormethod and the inner circumference side negative electrode activematerial layer 32 and the outer circumference side negative electrodeactive material layer 33 are formed.

Finally, the secondary battery is assembled using the positive electrode20 and the negative electrode 30. In such a case, in addition toattaching the positive lead 8 to the positive electrode collector 21 bywelding or the like, the negative lead 9 is attached to the negativeelectrode collector 31 by welding or the like. Next, after laminatingthe positive electrode 20, the separator 41, the negative electrode 30,and the auxiliary separator 42 in that order, the spirally woundelectrode body 10 is created by coiling the positive electrode 20, theseparator 41, the negative electrode 30, and the auxiliary separator 42so that the positive electrode 20 is arranged more to the innercircumference side than the negative electrode 30. Next, after insertinga center pin 51 into the coil opening portion 50 of the spirally woundelectrode body 10, the spirally wound electrode body 10 is placed insidethe battery casing 1 while being interposed by the pair of insulatingplates 2 and 3. In such a case, as well as attaching the positiveelectrode 8 to the safety valve mechanism 5 by welding or the like, thenegative lead 9 is attached to the battery casing 1 by welding or thelike. Next, the electrolyte solution is injected into the battery casing1 and impregnated into the separator 41 and the auxiliary separator 42.Finally, the battery lid 4, the safety valve mechanism 5, and theheat-sensitive resistance element 6 are caulked via the gasket 7 on theopening end portion of the battery casing 1.

[Actions and Effects of Secondary Battery]

Such a secondary battery includes the spirally wound electrode body 10in which the positive electrode 20 and the negative electrode 30 arelaminated via the separator 41, and the positive electrode 20, thenegative electrode 30, and the separator 41 are spirally wound with thecoil opening portion 50 as the center such that the positive electrode20 is arranged more on the inner circumference side than the negativeelectrode 30. The positive electrode 20 includes the inner circumferenceside positive electrode active material layer 22 and the outercircumference side positive electrode active material layer 23 that areformed on the positive electrode collector 21, and includes the singleside active material layer formation region 20Z on an end portion on theinner circumference side of the active material layer formation region20X in which the inner circumference side positive electrode activematerial layer 22 and the outer circumference side positive electrodeactive material layer 23 are formed. In particular, the ratio A/(A+B) ofthe area density A of the inner circumference side positive electrodeactive material layer 22 to the area density B of the outercircumference side positive electrode active material layer 23, theinner diameter C of the coil opening portion 50, the ratio D/E of thethickness D of the positive electrode 20 to the thickness E of thepositive electrode 21, and the length F of the single side activematerial layer formation region 20Z satisfy the relationships expressedin Formulae 1 and 2.

In such a case, as described above, the relationship between the areadensities A and B is optimized with the inner diameter C and therelationship between the thicknesses D and E, and the length F isoptimized with the relationship between the thicknesses D and E.Therefore, even if the inner diameter C is decreased (C=2.5 mm to 4 mm)in order to increase the volume occupied by the positive electrode 20within the secondary battery and the ratio D/E is increased (D/E=13.333to 20) in order to increase the volume occupied by the innercircumference side positive electrode active material layer 22 and theouter circumference side positive electrode active material layer 23within the positive electrode 20, fracturing of the positive electrode20 when coiling in the creation process of the spirally wound electrodebody 10 is suppressed, and the battery capacity and cyclecharacteristics are secured. It is therefore possible to obtainexcellent battery characteristics while suppressing fracturing of thepositive electrode 20 when coiling.

Furthermore, in order to suppress fracturing of the positive electrode20, there is no cause to include a copolymerization agent (binder) inthe inner circumference side positive electrode active material layer 22and the outer circumference side positive electrode active materiallayer 23 as described in the techniques of the related art. It istherefore possible to also suppress the loss of the inner circumferenceside positive electrode active material layer 22 and the outercircumference side positive electrode active material layer 23 whilesuppressing fracturing of the positive electrode 20.

In particularly, of the length F satisfies the relationship formulaexpressed in Formula 3, the cycle characteristics are able to be furtherimproved.

Further, even if a metallic material that is advantageous for a highcapacity on the one hand but which is prone to expansion and contractionwhen charging and discharging or a material that includes at least oneof silicon and tin in particular as the constituent element is used asthe negative electrode active material of the negative electrode 30, itis possible to suppress fracturing of the positive electrode 20 due tothe expansion and contraction of the negative electrode active materialduring charging and discharging.

<2. Uses of Secondary Battery>

Next, applied examples of the secondary battery described above will bedescribed.

As long as the uses of the secondary battery are a machine, anapparatus, a tool, a device, or a system (aggregate of a plurality ofapparatuses or devices) that is able to use the secondary battery aspower for driving or as a power storage source for accumulating electricpower, the uses of the secondary battery are not particularly limited.In a case when the secondary battery is used as a power source, thesecondary battery may be a main power source (power source that is usedpreferentially) or an auxiliary power source (power source that is usedinstead of the main power source or by switching from the main powersource). The type of main power source is not limited to secondarybatteries.

As the uses of the secondary battery, for example, the uses below areexemplified. Such uses are electronic apparatuses such as a videocamera, a digital still camera, a mobile phone, a notebook computer, acordless phone, a headphone stereo, a mobile radio, a mobile television,or a mobile information terminal (PDA: Personal Digital Assistant).However, electronic apparatuses are not limited to the electronicapparatuses for mobile use as described above, and may be non-mobile use(stationary) electronic apparatuses. The use of the secondary batteryincludes household instruments such as an electric shaver, a backupdevice, a storage device such as a memory card, electric tools such asan electric drill or a chain saw, medical apparatuses such as a pacemaker or a hearing aid, power sources such as a battery pack, electricvehicles such as an electric motorcar (including hybrid motorcars), andpower storage systems such as a household battery system in whichelectric power is accumulated in case of emergency.

Among such uses, the secondary battery is effective in being applied toa battery pack, an electronic apparatus, an electric tool, an electricvehicle, a power storage system, or the like. The reason is that sincethere is demand for excellent characteristics for the secondary battery(battery capacity, cycle characteristics, and the like), it is possibleto effectively improve such characteristics by using the secondarybattery of the embodiments of the disclosure. Here, the battery packincludes, along with the secondary battery, for example, a controlsection that controls the secondary battery and an outer packaging thatcontains the secondary battery. The electronic apparatus operates thesecondary battery as a power source for driving and executes varioustypes of functions. The electric tool moves a movable portion (forexample, a drill) with the secondary battery as the power source. Theelectric vehicle operates (travels) with the secondary battery as thepower source, and as described above, may be a motorcar that alsoincludes a power source other than the secondary battery (such as ahybrid motorcar). The power storage system is a system that uses thesecondary battery as a power storage source. For example, in a householdpower storage system, electric power is accumulated in the secondbattery that is a power storage source, and as the power that is storedin the secondary battery is consumed according to demand, various typesof apparatuses such as domestic electrical appliances become usable.

Examples

Examples of the embodiments of the disclosure will be described indetail.

Experiments 1 to 35

The cylindrical secondary battery (lithium ion secondary batter)illustrated in FIGS. 1 to 4B was created by the following steps.

First, the positive electrode 20 (thickness D: Tables 1 to 3) werecreated. In such a case, a lithium cobalt composite oxide (LiCoO₂) wasobtained by mixing lithium carbonate (Li₂CO₃) and cobalt carbonate(CoCO₃) in a molar ratio of Li₂CO₃:CoCO₃=0.5:1 and calcining in air(900° C.×5 hours). Next, after creating a positive electrode compound bymixing 91 parts by mass of the positive electrode active material(LiCoO₂), 3 parts by mass of the positive electrode binder(polyvinylidene fluoride), and 6 parts by mass of the positive electrodeconductive agent (graphite), the positive electrode compound wasdispersed in the solvent (N-methyl-2-pyrrolidone) to form the paste-likepositive electrode compound slurry. Finally, the inner circumferenceside positive electrode active material layer 22 and the outercircumference side positive electrode active material layer 23 wereformed by evenly applying the positive electrode compound slurry on bothsurfaces of the strip-like positive electrode collector 21 (aluminumfoil with the thickness E: Tables 1 to 3) using a bar coater beforebeing dried. In such a case, the single side active material layerformation region 20Z (length F (experimental values): Table 1 to 3) wasformed on an end portion on the inner circumference side of the activematerial layer formation region 20X. Next, the inner circumference sidepositive electrode active material layer 22 and the outer circumferenceside positive electrode active material layer 23 were compression moldedusing a roll press (area densities A and B and the ratio A/(A+B)(experimental values): Tables 1 to 3). Here, the theoretical values ofthe ratio A/(A+B) and the length F shown in Table 1 are respectivelyvalues that are derived from Formulae 1 and 2.

Next, the negative electrode 30 was created. In such a case, aftercreating a cobalt tin alloy powder by alloying cobalt powder and tinpowder, the cobalt tin alloy powder was dry blended by adding carbonpowder. Next, 20 g of the mixture was charged into a reaction containerof a planetary ball mill manufactured by Ito Seisakusho Co., Ltd. alongwith 400 g of corundum (diameter=9 mm) Next, after substituting theinside of the reaction container to an argon atmosphere, operating(rotation speed=250 rotations per minute, operation time=10 minutes) andpausing (pausing time=10 minutes) were repeated until the totaloperating time reached 30 hours. Next, after cooling the reactioncontainer to room temperature and retrieving the reactant(SnCoC-containing material), coarse grains were removed by passing thereactant through a sieve (280 mesh).

When the composition of the obtained SnCoC-containing material wasanalyzed, the tin content=49.9 mass %, the cobalt content=29.3 mass %,and the carbon content=19.8 mass %. In such a case, an inductivelycoupled plasma (ICP) emission analysis method for the tin and cobaltcontents and a carbon sulfur analyzer for the carbon content wererespectively used. Further, when the SnCoC-containing material wasanalyzed using the X-ray diffraction method, diffraction peaks withhalf-value widths within a range of diffraction angle 2θ=20° to 50° wereobserved. Furthermore, when the SnCoC-containing material was analyzedusing the XPS method, as illustrated in FIG. 5, a peak P1 was obtained.When the peak P1 was analyzed, a peak P2 of the surface contaminationcarbon and a peak P3 of C1s in the SnCoC-containing material on a lowerenergy side than the peak P2 (lower region than 284.5 eV) were obtained.From such results, it was verified that the carbon within theSnCoC-containing material was bound with the other elements.

After obtaining the SnCoC-containing material, 60 parts by mass of thenegative electrode active material (SnCoC-containing material), 10 partsby mass of the negative electrode binder (polyvinylidene fluoride), and30 parts by mass (artificial graphite=28 parts by mass, carbon black=2parts by mass) of the negative electrode conductive agent (artificialgraphite and carbon black) were mixed to form a negative electrodecompound before being dispersed in a solvent (N-methyl-2-pyrrolidone) toform a negative electrode compound slurry. Next, the inner circumferenceside negative electrode active material layer 32 and the outercircumference side negative electrode active material layer 33 wereformed by evenly applying the negative electrode compound slurry on bothsurfaces of the strip-like negative electrode collector 31 (aluminumfoil with thickness=15 μm) using a bar coater before being dried.Finally, the inner circumference side negative electrode active materiallayer 32 and the outer circumference side negative electrode activematerial layer 33 were compression molded using a roll press. In such acase, along with the difference in the area densities A and B betweenthe inner circumference side positive electrode active material layer 22and the outer circumference side positive electrode active materiallayer 23 in the positive electrode 20, the area densities of the innercircumference side negative electrode active material layer 32 and theouter circumference side negative electrode active material layer 33were respectively adjusted so that the balance of the charging anddischarging capacity between the positive electrode 20 and the negativeelectrode 30 that oppose each other becomes the same. Further, in orderthat the lithium metal does not precipitate toward the negativeelectrode 30 when in a fully charged state, the charging and dischargingcapacity of the negative electrode 30 was made larger than the chargingand discharging capacity of the positive electrode 20.

Next, after mixing ethylene carbonate (EC) and dimethyl carbonate (DMC)as the solvent, the electrolyte solution was prepared by dissolvinglithium hexafluorophosphate as the electrolytic salt. In such a case,the composition of the solvent (EC:DMC) was 30:70 by volume ratio, andthe density of the electrolytic salt was 1 mol/dm³ (=1 mol/l).

Finally, the secondary battery was assembled using the positiveelectrode 20, the negative electrode 30, and the electrolyte solution.In such a case, an aluminum positive electrode lead 8 was welded to thepositive electrode 20 (positive electrode collector 21), while a nickelnegative electrode lead 9 was welded to the negative electrode 30(negative electrode collector 31). Next, the positive electrode 20, theseparator 41 (micro-porous polyethylene film with thickness=20 μm), thenegative electrode 30, and the auxiliary separator 42 (same micro-porouspolyethylene as the separator 41) were laminated in that order. Next,after coiling the laminate body several revolutions with the coilingcore bar (outer diameter=inner diameter C of coil opening portion 50) asthe center such that the positive electrode 20 was arranged more to theinner circumference side than the negative electrode 30, the coilopening portion 50 (inner diameter C: Tables 1 to 3) was formed byextracting the coil core rod to create the spirally wound electrode body10 (outer diameter=17.1 mm) Next, after inserting the center pin 51 inthe coil opening portion 50, the spirally wound electrode body 10 wasplaced in a nickel-plated iron cylindrical battery casing 1 (diameter 18mm×height 65 mm) while being interposed by the pair of insulating plates2 and 3. Next, while the positive electrode lead 8 was welded to thesafety valve mechanism 5, the negative electrode lead 9 was welded tothe battery casing 1. Finally, after injecting the electrolyte solutioninto the battery casing 1 by a decompression method and impregnating inthe separator 41, the battery lid 4 was caulked on the battery casing 1via the gasket 7.

Upon investigating the coiling state and the battery characteristics(battery capacity and cycle characteristics) of the secondary battery inExperiments 1 to 35, the results shown in Tables 4 and 5 were obtained.

In a case when investigating the coiling state, in order to create thespirally wound electrode body 10, after coiling the positive electrode20 and the like with a core coil rod having the same outer diameter asthe inner diameter C and leaving for some amount of time, the spirallywound body was taken apart and the occurrence of fracturing of thepositive electrode 20 was ascertained by viewing. As a result, a casewhen there was no fracturing was marked by “◯” and a case whenfracturing occurred was marked by “×”.

In a case when investigating the battery capacity, after measuring thedischarging capacity by charging and discharging over one cycle in anatmosphere of 23° C., a standardized value (discharging capacity ratio)with the value of the discharging capacity measured in Experiment 23 asthe reference (100) was ascertained. As the charging and dischargingconditions, after charging by a constant current and a constant voltageto a maximum voltage 4.2 V by a current of 1 C, discharging by aconstant current was performed to an end voltage 2.5 V by a current of0.2 C. “1 C” and “0.2 C” are respectively current values that dischargethe theoretical capacity in one hour and five hours.

In a case when investigating the cycle characteristics, after measuringthe discharging capacity by charging and discharging over one cycle inan atmosphere of 23° C., the discharging capacity was measured byrepeating charging and discharging until the total number of cyclesbecame 300 cycles. From such a result, the capacity retention rate(%)=(discharging capacity at the 300th cycle/discharging capacity atfirst cycle)×100 was ascertained. With the exception of changing thecurrent value when discharging to 1 C, the charging and dischargingconditions were the same as when investigating the battery capacity.

Here, although it was possible to ascertain the discharging capacityratio and the capacity retention rate in a case when the positiveelectrode 20 did not fracture, since the secondary battery was not ableto charge and discharge in a case when the positive electrode 20 wasfractured, it was difficult to ascertain the discharging capacity ratioand the capacity retention rate.

TABLE 1 wNegative Electrode Active Material: SnCoC-Containing MaterialArea Area Ratio A/(A + B) Inner Length F (mm) Experiment Density ADensity B Experimental Theoretical Diameter Thickness Thickness RatioExperimental Theoretical Example (mg/cm²) (mg/cm²) Value Value C (mm) D(μm) E (μm) D/E Value Value 1 35.7 36.5 0.495 0.380 to 0.495 4 200 1513.333 5 5 to 50 2 35.7 36.5 0.495 0.380 to 0.495 4 200 15 13.333 50 5to 50 3 49.8 61.3 0.448 0.380 to 0.448 4 300 15 20 25 25 to 50 4 49.861.3 0.448 0.380 to 0.448 4 300 15 20 50 25 to 50 5 33.9 38.2 0.4700.380 to 0.472 2.5 200 15 13.333 5 5 to 50 6 33.9 38.2 0.470 0.380 to0.472 2.5 200 15 13.333 50 5 to 50 7 27.4 44.7 0.380 0.380 to 0.472 2.5200 15 13.333 5 5 to 50 8 37.7 44.2 0.460 0.380 to 0.461 2.5 225 15 15 87.5 to 50 9 39.5 48.3 0.450 0.380 to 0.455 2.5 240 15 16 10 9.8 to 50 1041.2 50.4 0.450 0.380 to 0.450 2.5 250 15 16.667 13 11.7 to 50 11 41.250.4 0.450 0.380 to 0.450 2.5 250 15 16.667 50 11.7 to 50 12 47.6 63.60.428 0.380 to 0.428 2.5 300 15 20 25 25 to 50 13 47.6 63.6 0.428 0.380to 0.428 2.5 300 15 20 50 25 to 50 14 42.2 68.9 0.380 0.380 to 0.428 2.5300 15 20 25 25 to 50 15 33.0 40.3 0.450 0.380 to 0.450 2.5 200 1216.667 13 11.7 to 50 16 38.1 50.9 0.428 0.380 to 0.428 2.5 240 12 20 2525 to 50 17 44.0 49.6 0.470 0.380 to 0.472 2.5 260 20 13.333 5 5 to 50

TABLE 2 Negative Electrode Active Material: SnCoC-Containing MaterialArea Area Ratio A/(A + B) Inner Length F (mm) Experiment Density ADensity B Experimental Theoretical Diameter Thickness Thickness RatioExperimental Theoretical Example (mg/cm²) (mg/cm²) Value Value C (mm) D(μm) E (μm) D/E Value Value 18 50.4 58.8 0.461 0.380 to 0.461 2.5 300 2015 8 7.5 to 50 19 34.6 37.5 0.480 0.380 to 0.480 3 200 15 13.333 5 5 to50 20 34.6 37.5 0.480 0.380 to 0.480 3 200 15 13.333 50 5 to 50 21 48.362.8 0.435 0.380 to 0.435 3 300 15 20 25 25 to 50 22 48.3 62.8 0.4350.380 to 0.435 3 300 15 20 50 25 to 50 23 26.3 26.3 0.500 0.380 to 0.5184 150 15 10 0 18 to 50 24 35.7 36.5 0.495 0.380 to 0.495 4 200 15 13.3330 5 to 50 25 35.7 36.5 0.495 0.380 to 0.495 4 200 15 13.333 100 5 to 5026 49.8 61.3 0.448 0.380 to 0.448 4 300 15 20 20 25 to 50 27 41.3 50.40.450 0.380 to 0.450 2.5 250 15 16.667 10 11.7 to 50 28 47.6 63.6 0.4280.380 to 0.428 2.5 300 15 20 22 25 to 50 29 38.9 72.2 0.350 0.380 to0.428 2.5 300 15 20 25 25 to 50

TABLE 3 Negative Electrode Active Material: SnCoC-Containing MaterialArea Area Ratio A/(A + B) Inner Length F (mm) Experiment Density ADensity B Experimental Theoretical Diameter Thickness Thickness RatioExperimental Theoretical Example (mg/cm²) (mg/cm²) Value Value C (mm) D(μm) E (μm) D/E Value Value 30 38.1 50.9 0.428 0.380 to 0.428 2.5 240 1220 22 25 to 50 31 50.4 58.8 0.461 0.380 to 0.461 2.5 300 20 15 0 7.5 to50 32 26.4 26.2 0.502 0.380 to 0.502 3 150 15 10 0 18 to 50 33 34.6 37.50.480 0.380 to 0.480 3 200 15 13.333 0 5 to 50 34 34.6 37.5 0.480 0.380to 0.480 3 200 15 13.333 100 5 to 50 35 48.3 62.8 0.435 0.380 to 0.435 3300 15 20 20 25 to 50

TABLE 4 Negative Electrode Active Material: SnCoC-Containing MaterialExperiment Occurrence of Discharge Capacity Example Fracturing CapacityRatio Retention Rate (%) 1 ∘ 108 86 2 ∘ 104 86 3 ∘ 114 82 4 ∘ 111 82 5 ∘113 86 6 ∘ 109 86 7 ∘ 113 80 8 ∘ 114 85 9 ∘ 115 85 10 ∘ 116 84 11 ∘ 11384 12 ∘ 118 82 13 ∘ 115 82 14 ∘ 118 80 15 ∘ 113 85 16 ∘ 116 84 17 ∘ 11684 18 ∘ 119 82 19 ∘ 108 85 20 ∘ 104 85 21 ∘ 114 81 22 ∘ 111 81 23 ∘ 10087 24 x — — 25 ∘ 100 85

TABLE 5 Negative Electrode Active Material: SnCoC-Containing MaterialExperiment Occurrence of Discharge Capacity Example Fracturing CapacityRatio Retention Rate (%) 26 x — — 27 x — — 28 x — — 29 ∘ 113  70 30 x —— 31 x — — 32 ∘ 86 87 33 x — — 34 ∘ 86 85 35 x — —

In a case when the ratio A/(A+B) and the length F satisfy therelationship expressed in Formulae 1 and 2 (Experiments 1 to 22),favorable results were obtained as compared to a case when suchconditions were not met (Experiments 23 to 35). Specifically, in thecase of the former, even if the inner diameter C is decreased and theratio D/E is increased (C=2.5 mm to 4 mm, D/E=13.333 to 20), fracturingof the positive electrode 20 was suppressed and a high dischargingcapacity ratio and capacity retention rate were obtained. In such acase, in particular, if the length F satisfies the relationshipexpressed in Formula 3, the capacity retention rate was even greater.

Experiments 36 to 43

When the coiling state and the battery characteristics were investigatedby creating the secondary battery by the same techniques as inExperiments 1 to 35 with the exception of using silicon (Si) instead ofthe SnCoC-containing material as the negative electrode active materialand setting the conditions as shown in Table 6, the results shown inTable 7 were obtained. Here, in a case when investigating the batterycapacity, the discharging capacity ratio was ascertained with the valueof the discharging capacity measured in Experiment 39 as the reference(100).

TABLE 6 Negative Electrode Active Material: Si Area Area Ratio A/(A + B)Inner Length F (mm) Experiment Density A Density B ExperimentalTheoretical Diameter Thickness Thickness Ratio Experimental TheoreticalExample (mg/cm²) (mg/cm²) Value Value C (mm) D (μm) E (μm) D/E ValueValue 36 27.1 30.6 0.470 0.380 to 0.472 2.5 160 12 13.333 5 5 to 50 3721.9 35.8 0.380 0.380 to 0.472 2.5 160 12 13.333 5 5 to 50 38 38.2 50.70.428 0.380 to 0.428 2.5 240 12 20 25 25 to 50 39 21.1 21.1 0.500 0.380to 0.518 4 120 12 10 0 18 to 50 40 28.9 28.9 0.500 0.380 to 0.495 4 16012 13.333 0 5 to 50 41 40.9 48.0 0.460 0.380 to 0.448 4 240 12 20 25 25to 50 42 40.0 48.9 0.450 0.380 to 0.448 4 240 12 20 20 25 to 50 43 28.329.4 0.490 0.380 to 0.472 2.5 160 12 13.333 5 5 to 50

TABLE 7 Negative Electrode Active Material: Si Experiment Occurrence ofDischarge Capacity Example Fracturing Capacity Ratio Retention Rate (%)36 ∘ 108 83 37 ∘ 108 80 38 ∘ 116 81 39 ∘ 100 83 40 x — — 41 x — — 42 x —— 43 x — —

Even when the type of the negative electrode active material waschanged, the same results as in Tables 1 to 5 were obtained.Specifically, in a case when the ratio A/(A+B) and the length Frespectively satisfy the relationships expressed in Formulae 1 and 2(Experiments 36 to 38), as compared to a case when such conditions arenot satisfied (Experiments 39 to 43), fracturing of the positiveelectrode 20 is suppressed and a high discharging capacity ratio andcapacity retention rate were obtained.

From the results of Tables 1 to 7 described above, it was verified thatwith the secondary battery of the embodiments of the disclosure, if thearea densities A and B, the inner diameter C, the thicknesses D and E,and the length F satisfy the relationships expressed in Formulae 1 and2, regardless of the type of negative electrode active material,fracturing of the positive electrode 20 when coiling is suppressed andexcellent battery characteristics are obtained.

Although the disclosure has been described above using the embodimentsand examples, the disclosure is not limited to the forms described bythe embodiments and the example, and various modifications are possible.For example, the secondary battery of the embodiments of the disclosureis similarly able to be applied to a secondary battery in which thecapacity of the negative electrode includes a capacity by the absorptionand discharging of lithium and a capacity that accompanies theprecipitation dissolution of lithium and which is represented by the sumof such capacities. In such a case, while a negative electrode materialthat is able to absorb and discharge lithium is used as the negativeelectrode material, the chargeable capacity of the negative electrodematerial is set to be less than the dischargeable capacity of thepositive electrode.

Further, although a case when the battery structure is cylindrical hasbeen exemplified and described in the embodiments and examples, thebattery structure is not limited thereto, and the secondary battery issimilarly able to be applied in a case when the secondary battery has adifferent battery structure such as a square.

Further, although a case when lithium is used as the element of thecarrier has been described in the embodiments and the examples, thecarrier is not limited thereto. The carrier may, for example, be otherGroup 1 elements such as sodium (Na) or potassium (K), may be Group 2elements such as magnesium or calcium, or may be other light metals suchas aluminum. Since the effects of the embodiments of the disclosure areable to be obtained regardless of the type of element of the carrier,the same effects are obtained even when the type of element is changed.

Further, in the embodiments and examples, with regard to the range ofthe ratio A/(A+B), an appropriate range derived from the results of theexamples have been described. Such a description is not to completelydeny the possibility that the ratio A/(A+B) falls outside of the rangedescribed above. That is, since the appropriate range described above ismerely a range that is particularly preferable in obtaining the effectsof the embodiments of the disclosure, as long as the effects of theembodiments of the disclosure are obtained, the ratio A/(A+B) maydeviate somewhat from the range described above. The same is also trueof the length F.

It should be understood that various changes and modifications to thepresently preferred embodiments described herein will be apparent tothose skilled in the art. Such changes and modifications can be madewithout departing from the spirit and scope of the present subjectmatter and without diminishing its intended advantages. It is thereforeintended that such changes and modifications be covered by the appendedclaims.

The invention is claimed as follows:
 1. A secondary battery comprising:an electrode body in which a positive electrode and a negative electrodeare laminated via a separator and wound with a coil opening portion ofthe electrode body as a center, wherein the positive electrode includesa first positive electrode active material layer formed on a first sideof a positive electrode collector and a second positive electrode activematerial layer formed on a second side of the positive electrodecollector, and wherein a ratio A/(A+B) of an area density A (mg/cm²) ofthe first positive electrode active material layer and an area density B(mg/cm²) of the second positive electrode active material layer, aninner diameter C (mm) of the coil opening portion, and a ratio D/E of athickness D (μm) of the positive electrode and a thickness E (μm) of thepositive electrode collector satisfy a relationship expressed below:0.380≦A/(A+B)≦[0.593−0.007×(D/E)]×(0.03×C+0.87) wherein C is 2.5≦C≦4 andD/E is 13.333≦D/E≦20.
 2. The secondary battery according to claim 1,wherein the first positive electrode active material layer is formed onan inner circumference side of the positive electrode collector, and thesecond positive electrode active material layer is formed on an outercircumference side of the positive electrode collector.
 3. The secondarybattery according to claim 1, which further satisfies a relationshipexpressed below:0.428≦A/(A+B)[0.593−0.007×(D/E)]×(0.03×C+0.87).
 4. The secondary batteryaccording to claim 1, wherein the negative electrode includes a negativeelectrode active material comprising at least one of silicon and tin. 5.The secondary battery according to claim 1, wherein the negativeelectrode includes a negative electrode active material comprising tin,cobalt, and carbon, and wherein an amount of carbon in the negativeelectrode active material is equal to or greater than 9.9 mass % andequal to or less than 29.7 mass %, an amount of cobalt to a total amountof tin and the cobalt in the negative electrode active material is equalto or greater than 20 mass % and equal to or less than 70 mass %, and ahalf-value width of a diffraction peak that is obtained by X-raydiffraction of the negative electrode active material is equal to orgreater than 1°, and wherein a diffraction angle 2θ is equal to orgreater than 20° and equal to or less than 50°.
 6. The secondary batteryaccording to claim 1, which is a lithium ion secondary battery.
 7. Abattery pack comprising: the secondary battery according to claim 1; acontrol section that controls the secondary battery; and an outerpackaging that contains the secondary battery.
 8. An electronicapparatus comprising the secondary battery according to claim 1 as apower source.
 9. An electric tool comprising the secondary batteryaccording to claim 1 as a power source.
 10. An electric vehiclecomprising the secondary battery according to claim 1 as a power source.11. A power storage system comprising the secondary battery according toclaim 1 as a power storage source.
 12. The secondary battery accordingto claim 1, wherein the positive electrode includes a single side activematerial layer formation region in which the second positive electrodeactive material layer is formed on a single side of an end portion ofthe positive electrode collector, and wherein a length F (mm) of thesingle side active material layer formation region satisfies arelationship expressed below:[0.3×(D/E)²−7×(D/E)+45]≦F≦50.
 13. A secondary battery comprising: anelectrode body in which a positive electrode and a negative electrodeare laminated via a separator and wound with a coil opening portion ofthe electrode body as a center, wherein the positive electrode includesa first positive electrode active material layer formed on a first sideof a positive electrode collector and a second positive electrode activematerial layer formed on a second side of the positive electrodecollector, wherein the positive electrode includes a single side activematerial layer formation region in which the second positive electrodeactive material layer is formed on a single side of an end portion ofthe positive electrode collector, and wherein a ratio D/E of a thicknessD (μm) of the positive electrode and a thickness E (μm) of the positiveelectrode collector and a length F (mm) of the single side activematerial layer formation region satisfy a relationship expressed below:[0.3×(D/E)²−7×(D/E)+45]≦F≦50.
 14. The secondary battery according toclaim 13, wherein the first positive electrode active material layer isformed on an inner circumference side of the positive electrodecollector, and the second positive electrode active material layer isformed on an outer circumference side of the positive electrodecollector.
 15. The secondary battery according to claim 13, wherein thenegative electrode includes a negative electrode active materialcomprising at least one of silicon and tin.
 16. A battery packcomprising: the secondary battery according to claim 13; a controlsection that controls the secondary battery; and an outer packaging thatcontains the secondary battery.
 17. An electronic apparatus comprisingthe secondary battery according to claim 13 as a power source.
 18. Anelectric tool comprising the secondary battery according to claim 13 asa power source.
 19. An electric vehicle comprising the secondary batteryaccording to claim 13 as a power source.
 20. A power storage systemcomprising the secondary battery according to claim 13 as a powerstorage source.